In power electronics equipment such as inverters for electric vehicles and hybrid vehicles and inverters for railway vehicles, a reduction in size and cost of a power semiconductor device (power module) which is a core component is demanded. One method for achieving the reduction in size and cost is to increase an operable temperature of a power semiconductor element.
When the operable temperature of the power semiconductor element is increased, a current value per unit area that can be input into the element increases. As a result, the power semiconductor element and the power semiconductor device can be reduced in size, and with the reduction in size, the manufacturing cost of the power semiconductor device can be reduced.
On the other hand, when the operable temperature of the power semiconductor element is increased, a thermal stress generated in the power semiconductor device due to a difference in thermal expansion coefficient between the power semiconductor element and a wiring portion increases. As a result, the thermal stress concentrates on a connecting portion (on-chip bonding portion) that connects the power semiconductor element and the wiring portion, which leads to deterioration in thermal fatigue durability of the connecting portion.
As the technique for increasing the thermal fatigue durability of such an on-chip bonding portion, the following technique is known, for example.
Japanese Patent Laying-Open No. 2010-10502 discloses a semiconductor module in which an electrode of a power semiconductor element and a wiring portion are bonded by a silver (Ag)-based bonding layer.
Japanese Patent Laying-Open No. 2005-19694 discloses a power module in which a stacked body is inserted between an electrode portion of a chip and a terminal portion (wiring portion). The stacked body is formed of two low deformation resistive elements acting as stress buffering members, and a low thermal expansion element disposed between the two low deformation resistive elements and having a thermal expansion coefficient lower than a thermal expansion coefficient of the low deformation resistive elements. The electrode portion and one low deformation resistive element of the stacked body are bonded with an intermetallic compound layer mainly composed of Sn and Ni being interposed, and the other low deformation resistive element of the stacked body and the terminal portion are also bonded with an intermetallic compound layer mainly composed of Sn and Ni being interposed. The intermetallic compound layers have an equivalent configuration.